Glutarimidedioxime:\nA Complexing, Reductive, and Nitrosyl\nReagent for Molybdenum

Glutarimidedioxime\nis a cyclic amidoxime moiety formed\nduring the\nsynthesis of amidoxime-functionalized fibers and apparently facilitates\nthe extraction of uranium from seawater. Herein, we comprehensively\nexplore differences between molybdenum and vanadium coordinated by\nglutarimidedioxime. The high adsorption of vanadium is explained by\nthe formation of rare nonoxido vanadium(V) complexes, where each bare\nV<sup>5+</sup> is coordinated with two tridentate glutarimidedioxime\nligands. By contrast, molybdenum is coordinated by only one glutarimidedioxime\nligand, and the oxido MoO bonds in molybdate cannot be displaced\nby the ligand. Under seawater conditions, vanadium is fully complexed.\nMeanwhile, approximately 25% of molybdenum ions are in the form of\nfree molybdate even if the concentration of glutarimidedioxime is\n100000 times that of molybdenum. Glutarimidedioxime was expected to\nbe more stable in the presence of metal ions than without them. However,\ncomplexation with molybdenum accelerated the degradation of the glutarimidedioxime\nligand to release hydroxylamine. Molybdenum(VI) was then reduced by\nhydroxylamine, which itself was oxidized into nitrosyl. Vanadium heavily\noutcompetes adsorption of uranium, while molybdenum causes the degradation\nof glutarimidedioxime; the latter issue has previously been neglected\nand was first reported here.